Abstract: The optimum design of TBM mucking slot under certain open area was studied. By introducing the discrete element method， we took design parameters of mucking slot and its quantitiess as variables， and made a series of TBM rock ballast liquidity simulation experiments. We proposed a design method of mucking slot providing the same opening area of the cutterhead. First， the design should use the symmetrical arrangement as possible. Second， it should be more rational as long as the arrangement of alternating between long and short mucking slot is used. Third， the width of long mucking slot should be decreased for the stability of discharging ballasts. Take the numerical simulation results of the Yintao project comparing with the original design as an example， the efficiency and stability of discharging ballasts has been increased by 15.08% and 11.97%， respectively.

Key words: TBM, mucking slot, DEM(discrete element method), PFC, open area